What is the significance of molecular remission in multiple myeloma?

The present definition of complete remission (CR) in myeloma is not adequate. The definition is mainly based on measuring the secreted product of myeloma cells (M protein), which has a high interpatient and intrapatient variability, rather than on direct measurement of the remaining tumor load. Polymerase chain reaction (PCR) techniques are very sensitive to measure minimal residual disease, but in myeloma such a technique is very costly and labor intensive because a specific probe needs to be generated for each patient. There is preliminary evidence, based on a limited number of patients analyzed, that specific PCRs are better predictors of outcome in myeloma than the presently used definition of hematologic CR. Our limited experience indicates that with intensive therapy, including tandem transplants, a high percentage of patients in hematologic CR also achieve a molecular CR. The time to disease progression of such patients appears to be significantly longer compared to that of patients not achieving a molecular CR.